Phenolic resin curatives for EPDM, butyl rubber, natural rubber, and synthetic rubber from conjugated diene monomers or combinations thereof are known. The use of phenolic curatives in combinations with EPDM, butyl rubber, natural rubber, and synthetic rubber from conjugated diene monomers in thermoplastic elastomers is also known.
The structure of phenolic resins used in the curing of elastomers varies depending on the reaction conditions used to prepare them. Resole resins hare 2 types of structures between aromatic rings, dibenzyl ether and/or methylene links. Dibenzyl ether links are preferably formed under basic conditions and lower reaction temperatures. Methylene bridge links are preferably formed under acidic conditions and higher reaction temperatures. Both structures, however, are typically formed in resole resin synthesis. According to textbooks such as George Odian's "Principles of Polymerizations" 2nd ed. @ pp. 128-133, the relative importance of the phenolic resin (resole resin) structure has not been well established. However, publications such as Applications of a Cone/Plate Rheometer for the Characterization of Resol-Type Phenol Formaldehyde Resins by Solomon So et al., Journal of Polymer Science, Applied Polymer Symposium 51, 227-291(1992) pages 287-289 teach that resol-type phenol formaldehyde resins having a higher level of methylene bridges possess shorter cure times.
Resole resins having high or exclusively methylene linkages are preferred for elastomer vulcanization in the thermoset rubber industry.